The present invention relates to a composite train housing for pseudo-planetary kinematic transmission.
Known coaxial kinematic transmissions that need to obtain ratios of more than 7-8 by using simple sun-and-planet gear systems generally entail the adoption of multiple reduction (or step-up) stages if trains of the type shown in FIG. 1 of the accompanying drawings are adopted.
In FIG. 1, X1 and X2 designate the shafts between which motion is transmitted (speeds {overscore (ω)}1 and {overscore (ω)}2), A designates the sun gear, B designates the internal ring gear, a and b designate the planet gears, and the train housing is designated by U.
There are still good possibilities of execution, for average ratios which are in any case higher than those possible with the type shown in FIG. 1, when using trains of the type shown in FIG. 2 (in which the same terms are used), in which the planet gears a and b are coupled, with the advantage of obtaining the required ratio with a single set instead of two trains of FIG. 1 arranged in a cascade configuration.
Furthermore, in the case of FIG. 2 a single internal ring gear is used, whereas it is difficult to manufacture planet gears a and b of very high precision as regards the phasing between the toothed bands, in order to ensure correct meshing with the mating gears.
If one wishes to use a sun-and-planet gear system in high-speed transmissions, it is currently necessary to keep the train housing or spider U motionless, in order to avoid centrifugal stresses on the planet gears a and b and especially on the bearings of the planet gears.
In the case of a fixed train housing or spider U and of rotating sun gear A and internal ring gear B, the reduction train is termed pseudo-planetary.
This is true both for the type shown in FIG. 1 and for the type shown in FIG. 2.
A characteristic of this solution is the opposite direction of rotation between the input and the output.
A considerable limitation to the production of a pseudo-planetary train of the type shown in FIG. 2 is constituted by the limited space available for providing a rigid structure for the train housing U, which is formed monolithically, with particular reference to the posts that connect the two shoulders of said train housing, as shown in particular in FIGS. 3 and 4 (which are diametrical and transverse sectional views of a reduction unit), in which the posts are designated by M and the shoulders are designated by S.
This limitation is linked to the need to join the two shoulders S by passing close to both series of planet gears a and b and remaining within the addendum circle of the internal set of teeth B.
The result is a highly convoluted shape of the posts M that is almost always very narrow if not entirely insufficient.
The problem of the assembly of the various components is also very difficult and sometimes even impossible.
Moreover, it is impossible to adopt large bearings, whose presence would be sometimes desirable.